1. Field of the Invention
The present invention relates to a recording medium, and more precisely relates to a recording medium which has an electroconductive substrate and recording layer resistant to high humidity and wetting, and provides high precision visual images and color reproduction of superior quality.
2. Background Art
Electrostatic recording media are now widely used for monochrome and color printing in various automated office apparatuses such as computer printers, facsimile machines, drafting apparatuses, newspaper editors, and other kinds of recording apparatuses. In order for these apparatuses to function reliably, a recording medium which has a strong resistance to humidity and wetting has been in high demand. This demand becomes even greater when the recording medium is used outdoors.
In addition, the electrostatic recording medium is widely used in CAD-CAM systems which have become increasingly popular. Also, since the electrostatic recording medium is compatible with a color image display, the electrostatic medium can be widely used in various design and advertisement businesses. As a consequence of the increasing field of application, there has been an increasing demand for higher precision electrostatic recording medium.
A conventional electrostatic recording medium comprises an electroconductive substrate and a recording layer formed on the substrate. The electroconductive substrate includes a base sheet and an electroconductive layer laid on the base sheet, or a base sheet and an electroconductive material dispersed in the base sheet. In a typical example of a conventional electrostatic recording medium, as described in Japanese Patent Application First Publication No. 61-264345, a base sheet which is made from water resistant paper, resin film, or cloth and an electroconductive layer containing an electrolyte such as a cation polyelectrolyte comprising amino group. The electrical resistance of such conventional electroconductive substrates is not very sensitive to humidity. However, when the recording medium is wetted during use outdoors, the water soluble electrolyte tends to be washed out and consequently the recording layer tends to exfoliate. Furthermore, the conventional recording layer is sensitive to humidity, and the visual image produced thereby tends to be degraded when the medium is used in a humid environment. Therefore, the requirement for reliable service in an environment containing high humidity and wetting has not been satisfied by conventional electrostatic recording media. Furthermore, the images produced by conventional electrostatic recording media tend to become uneven, and also sometimes undesired white blots are produced due to the unevenness of the pigment particle size. Therefore, the conventional electrostatic recording media do not satisfy the demands for fine precision and color reproduction.